Influence of Bifurcation Structures Revealed by Refinement of a Nonlinear Conductance in JosephsonJunction Element

We conduct a bifurcation analysis of a single-junction superconducting quantum interferometer with an external flux. We approximate the current-voltage characteristics of the conductance in the equivalent circuit of the JJ by using two types of functions: a linear function and a piecewise linear (PWL) function. We describe a method to compute the local stability of the solution orbit and to solve the bifurcation problem. As a result, we reveal the bifurcation structure of the systems in a two-dimensional parameter plane. By making a comparison between the linear and PWL cases, we find a difference in the shapes of their bifurcation sets in the two-dimensional parameter plane even though there are no differences in the one-dimensional bifurcation diagrams or the trajectories. As for the influence of piecewise linearization, we discovered that grazing bifurcations terminate the calculation of the local bifurcations, because they drastically change the stability of the periodic orbit.

Structural and Ferromagnetic Properties SnO2/TiO2 Nanotubes Obtained by Electrospinning

SnO2/TiO2 (Sn/Ti [Formula: see text]/1) nanotubes were prepared by the electrospinning method. The morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the inner diameter of prepared materials was about 100[Formula: see text]nm and the wall thickness was about 10[Formula: see text]nm. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) showed that SnO2/TiO2 nanotubes had a mixed phase of SnO2 rutile and TiO2 anatase structures and no impurity phases. The magnetic properties of the SnO2/TiO2 nanotubes were characterized by a superconducting quantum interferometer (SQUID). The results indicated that the samples exhibited room temperature ferromagnetism which may be attributed to the interface between TiO2 and SnO2 phases.